As a result of recent engine developments, the intake manifolds on traditionally diesel applications and other internal combustion engines have become turbo charged or pressurized with natural gas fuel mixtures. Prior to these developments, such engines had vacuums without fuel in their intakes. This recent modification creates the hazard of explosions within the intake manifold. For example, backfires from the cylinders or hot spots on the intake valves can ignite the fuel mixture in the intake. Consequently, the excess pressure within the intake manifold created by the explosion may cause damage to the engine.